Why is there noise in my output?
Blender Internal

If you're using Blender Internal with Raytracing as your Gather mode, the following will work. Raytracing is realistic, but it requires a certain number of samples, otherwise it will be grainy.

In the World settings in the Gather section, change the samples to something like 10 or 12:


Cycles

If you're using Cycles, you can turn up the render samples in the Render panel under sampling: